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Matter and Minerals. From the movie: Honey I shrunk the Geologist. Minerals: Building blocks of rocks. Definition of a mineral : Naturally occurring Inorganic solid Ordered internal molecular structure Definite chemical composition Definition of a rock :
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Matter and Minerals From the movie: Honey I shrunk the Geologist
Minerals: Building blocks of rocks • Definition of a mineral: • Naturally occurring • Inorganic solid • Ordered internal molecular structure • Definite chemical composition • Definition of a rock: • A solid aggregate or mass of minerals
Composition of Elements • Atomic structure • Central region called the nucleus • Consists of protons (positive charges) and neutrons (neutral charges) • Electrons • Negatively charged particles that surround the nucleus • Located in discrete energy levels called shells
Composition of minerals • Chemical bonding • Formation of a compound by combining two or more elements • Ionic bonding • Atoms gain or lose outermost (valence) electrons to form ions • Ionic compounds consist of an orderly arrangement of oppositely charged ions
Composition of minerals • Covalent bonding • Atoms share electrons to achieve electrical neutrality • Covalent compounds are generally stronger than ionic bonds • Both ionic and covalent bonds typically occur in the same compound (bonds are seldom 100% ionic or covalent in character)
Composition of minerals • Isotopes and radioactive decay • Mass number is the sum of neutrons plus protons in an atom • An isotope is an atom that exhibits variation in its mass number • Some isotopes have unstable nuclei that emit particles and energy in a process known as radioactive decay
Structure of minerals • Minerals consist of an orderly array of atoms chemically bonded to form a particular crystalline structure • For ionic compounds, the internal atomic arrangement is primarily determined by the size of ions involved
Structure of minerals • Polymorphs • Two or more minerals with the same chemical composition but different crystalline structures • Diamond and graphite are good examples of polymorphs • The transformation of one polymorph to another is called a phase change • Example: Peanut Butter in a high pressure cell makes Diamond - or Grandma, for that matter! • http://www.lifegem.com/secondary/LifeGemFAQ2006.aspx#remainsorashes
Diamond & graphite – polymorphs of carbon
Given that diamond and graphite are made of the same element (carbon), why do you think each one has such different properties? • Carbon atoms have different shapes in graphite than in diamond and thus don’t bond as well • Diamond is formed in the mantle under high pressures which bonds it together more strongly C. Graphite is formed later in Earth’s history when gravity is lower D. When diamond is polished into gemstones, it becomes clearer and harder E. Diamonds are a girls best friend, which makes them harder to get
Physical properties of minerals • Crystal Form • External expression of the orderly internal arrangement of atoms • Crystal growth is often interrupted because of competition for space and rapid loss of heat • Note this isn’t cleavage!
Physical properties of minerals • Luster • Appearance of a mineral in reflected light • Two basic categories • Metallic • Nonmetallic • Other terms are used to further describe luster such as vitreous (oily), silky, or earthy (like dirt)
Physical properties of minerals • Color • Generally an unreliable diagnostic property to use for mineral identification • Often highly variable for a given mineral due to slight changes in mineral chemistry • Exotic colorations of some minerals produce gemstones • But we use it anyway :-o)
Question: How would you know all these samples are the same type of mineral (quartz)? They have specific colors common only in quartz They have the same crystal shape, or habit, related to composition + bonding They reflect light similarly They were all collected in the same place (in this case a mine) None of the above
Physical properties of minerals • Streak • Color of a mineral in its powdered form • Helpful in distinguishing different forms of the same mineral • Hardness • Resistance of a mineral to abrasion or scratching • All minerals are compared to a standard scale called the Mohs scale of hardness
Physical properties of minerals • Cleavage • Tendency to break along planes of weak bonding • Produces flat, shiny surfaces • Described by resulting geometric shapes • Number of planes • Angles between adjacent planes
Three examples of perfect cleavage – fluorite, halite, and calcite
Micas have perfect cleavage muscovite
Physical properties of minerals • Fracture • Absence of cleavage when a mineral is broken • Specific Gravity • Ratio of the weight of a mineral to the weight of an equal volume of water • Average value is approximately 2.7 • Simply hefting a mineral works too.
Physical properties of minerals • Other properties • Magnetism • Reaction to hydrochloric acid • Malleability • Double refraction • Taste • Smell • Elasticity
The main difference between minerals and rocks is ________. • minerals are smaller than rocks • B. people eat rocks in their vitamins, but don’t generally eat minerals • C. minerals have a particular chemical composition and ordered internal structure, whereas rocks are more complicated because they are mixtures of minerals • D. rocks have a particular chemical composition and ordered internal structure, whereas minerals are mixtures of rocks • E. minerals and rocks are the same thing; there is no major difference
You are hiking in Rocky Mountain Natl Park and pick up a rock. How would you go about identifying minerals in it? Look for original crystal faces Try to estimate its density C. Break it to determine how it cleaves Try to scratch it All of the above
Classification of Minerals • Nearly 4000 minerals have been identified on Earth (most of which we don’t really worry about). • Rock-forming minerals • Common minerals that make up most of the rocks of Earth’s crust • Only a few dozen members • Composed mainly of the 8 elements that make up 98% of the continental crust
Classification of Minerals • Silicates • Most important mineral group • Comprise most of the rock-forming minerals • Very abundant due to large amounts of silicon and oxygen in Earth’s crust • Basic building block is the silicon-oxygen tetrahedron molecule • Four oxygen ions surrounding a much smaller silicon ion
Classification of Minerals • Silicate structures • Single tetrahedra are linked together to form various structures including • Isolated tetrahedra • Ring structures • Single and double chain structures • Sheet or layered structures • Complex 3-dimensional structures
Be sure you can identify all the minerals on this chart Olivene Pyronene Amphibole Biotite Muscovite Orthoclase Plagioclase Quartz
The basic building blocks of silicate minerals are… a. Long chains of silicon atoms b. A series of SiH2 molecules bonded together c. A series of SiH4 molecules bonded together d. A series of SiO2 molecules bonded together e. A series of SiO4 molecules bonded together
Classification of Minerals • Common Silicate minerals • Olivine • High temperature Fe-Mg silicate (mantle mineral - formed 100’s km in Earth • Individual tetrahedra linked together by iron and magnesium • Forms small, rounded crystals with no cleavage peridot
Classification of Minerals • Common Silicate minerals • Pyroxene Group • Single chain structures involving iron and magnesium • Two distinctive cleavages at nearly 90 degrees • Augite is the most common mineral in the pyroxene group
Classification of Minerals • Common Silicate minerals • Amphibole Group • Double chain structures involving a variety of ions • Two perfect cleavages exhibiting angles of 124 and 56 degrees • Hornblende is the most common mineral in the amphibole group
Classification of Minerals • Common Silicate minerals • Mica Group • Sheet structures that result in one direction of perfect cleavage • Biotite is the common dark colored mica mineral • Muscovite is the common light colored mica mineral
